In recent years, various uses of high-function magnetic sensor LSIs with magnetic detection elements (such as Hall elements or magneto resistance elements) and a signal processing circuit (i.e., LSI) integrated together have been promoted. For example, in automobiles, there is a rotation angle sensor for detecting a rotation angle of a steering wheel. PTL 1, for example, proposes such a rotation angle sensor. PTL 1 discloses a rotation angle sensor using a magnetic flux concentrator for collecting and amplifying surrounding magnetic fields and Hall elements on a silicon substrate.
FIG. 1 is a configuration diagram illustrative of the rotation angle sensor described in PTL 1. The rotation angle sensor includes a rotating magnet 1 attached to a rotor and an integrated circuit (i.e., silicon substrate) 2 disposed under the rotating magnet 1 separated from the rotating magnet 1. On the silicon substrate 2, Hall elements 3 formed on the silicon substrate 2 and a magnetic flux concentrator 4 formed on the Hall elements 3 are provided. A magnetic field (i.e., transverse magnetic field) parallel to a plane of the silicon substrate 2 generated by the rotating magnet 1 is detected by using the magnetic flux concentrator 4 and the Hall elements 3, so that a rotation angle of the rotating magnet 1 is calculated.
FIG. 2 is a diagram illustrative of an arrangement of the Hall elements and the magnetic flux concentrator formed on the silicon substrate as illustrated in FIG. 1. Supposing that a plane parallel to the silicon substrate 2 is an XY plane, the circular magnetic flux concentrator 4 is arranged around an origin on the XY plane. Four Hall elements 3 are arranged under a circumference forming an edge of the magnetic flux concentrator 4. The Hall elements (H0, H180) 3 are arranged in symmetrical positions about the origin on the X axis. In the same way, The Hall elements (H90, H270) 3 are arranged in symmetrical positions about the origin on the Y axis. The H0 and H90 Hall elements are arranged in positions having positive coordinate components on the XY coordinate plane in FIG. 2.
FIG. 3 is a cross-sectional view illustrative of the rotating magnet, the magnetic flux concentrator, the Hall elements, and the silicon substrate illustrated in FIG. 1 taken along an X axis direction. A direction extending vertically from the silicon substrate 2 toward the rotating magnet 1 is a Z axis positive direction. A direction extending from H180 toward H0 is an X axis positive direction. Furthermore, two Hall elements are illustrated in positions symmetrical about a center of the magnetic flux concentrator 4 under the edge of the magnetic flux concentrator 4. Magnetosensitive planes of the Hall elements H0 and H180 are perpendicular to the plane of the silicon substrate 2. Therefore, each of the Hall elements H0 and H180 detects a magnetic field in a Z axis direction.
As illustrated in FIG. 3, however, a magnetic field generated from the rotating magnet 1 is attracted to the magnetic flux concentrator 4. A transverse magnetic field parallel to the plane of the silicon substrate 2 (an X axis component of the magnetic field in FIG. 3) is bent to a direction (Z axis direction) perpendicular to the plane of the silicon substrate 2 and passes through the magnetosensitive planes of the Hall elements. Therefore, it is possible for these Hall elements to detect the transverse magnetic field as a signal.
With such a configuration, the Hall elements H0 and H180 illustrated in FIG. 2 detect an X axis component and a Z axis component of a magnetic field incident on the magnetic flux concentrator 4. In the same way, H90 and H270 detect a Y axis component and the Z axis component.
FIG. 2 illustrates a state in which a magnetic field is incident on the magnetic flux concentrator 4 in a direction of θ counterclockwise from the X axis about the origin. It is supposed that H0 detects the X axis component of the magnetic field as a positive sign output (+Vx) and H180 detects the X axis component of the magnetic field as a negative sign output (−Vx) at this time. In the same way, it is supposed that H90 detects the Y axis component of the magnetic field as a positive sign output (+Vy) and H270 detects the Y axis component of the magnetic field as a negative sign output (−Vy). It is supposed that all of the four Hall elements detect the Z axis component of the magnetic field by regarding a direction of incidence on the XY plane as a positive sign output (+Vz).
Therefore, signals HVX and HVY detected respectively as a difference between the output of H0 and the output of H180 and a difference between the output of H90 and the output of H270 becomeHVX=+Vx+Vz−(−Vx+Vz)=2Vx  (1)HVY=+Vy+Vz−(−Vy+Vz)=2Vy  (2)
In other words, the signals HVX and HVY represent the X axis component and the Y axis component of a magnetic field strength, respectively. The Z axis component is canceled and is not detected.
The rotation angle sensor calculates the angle θ of the magnetic field from HVX and HVY asθ=a tan(HVY/HVX)  (3)
The reason why the angle is calculable in this way is that the magnetic field strength under the magnetic flux concentrator with respect to the rotating magnetic field exhibits an ideal sinusoidal change.
FIG. 4 is a block configuration diagram illustrative of signal processing in the rotation angle sensor described in PTL 1. The rotation angle sensor includes the Hall elements H0, H180, H90 and H270, an X axis subtraction unit 11X for subtracting detection signals of H0 and H180, a Y axis subtraction unit 11Y for subtracting detection signals of H90 and H270, and an arithmetic operation unit 12 for calculating the angle from an output (Expression (1)) of the X axis subtraction unit 11X and an output (Expression (2)) of the Y axis subtraction unit 11Y by using Expression (3).
PTL 2 describes an angle calculation technique. The angle calculation technique does not use the XY coordinate system described above. In plural Hall elements arranged under a circumference of a magnetic flux concentrator at equal intervals, an angle is calculated from outputs from two adjacent Hall elements differing in signal output sign.
Such a rotation angle sensor poses a problem of an error between the calculated angle and an angle of a rotating magnetic field to be detected caused by offsets of the Hall elements, offsets of amplifiers for amplifying signals fed from the Hall elements, or a difference in gain between the X axis and the Y axis. Several solutions have been presented. PTL 3, for example, reduces the offsets of the Hall elements by arranging the Hall elements under the magnetic flux concentrator to yield reflected image relations. PTL 4, for example, reduces the angle error by performing coordinate conversion on an X component signal and a Y component signal detected respectively by magnetic sensors arranged on the X axis and the Y axis.
Further, PTL 5, for example, discloses a technique for reducing an angle error generated by the magnetic field distortion of an external magnet. A rotation angle sensor described in PTL 5 reduces an error of an MR (i.e., magnetic resistance) element or an error caused by a magnetic field distortion of the external magnet.
Moreover, PTL 6, for example, discloses a technique of computing each axis component by using a magnetic flux concentrator and at least two Hall elements.